1. Field of the Invention
The present invention relates to a method of forming a semiconductor device by activating a semiconductor region with laser light.
2. Description of the Prior Art
Thin film semiconductor devices such as insulated gate thin film field effect transistors (TFTs) have been manufactured by introducing high energy ions into silicon semiconductor films by the ion implantation technique, the plasma doping technique and the like in order to form impurity semiconductor regions. The crystallinity of the semiconductor regions is substantially damaged due to the shock of the ion bombardment during the implantation. The crystallinity of the semiconductor regions must be recovered, e.g., by exposing the semiconductor regions to appropriate light emitted from a laser, a lamp or another suitable light source so that the impurity elements are activated in the semiconductor regions to accord necessary carrier transportation characteristics to them. Because of this, there is a need for a suitable technique by which laser annealing can be utilized for forming the insulated gate thin film field effect transistors since laser annealing is particularly suitable and advantageous for mass-production of semiconductor devices. Particularly, pulsed laser light can be used to effectively heat only the surface portion of the semiconductor region so that improvement of the productivity is expected.
The recrystallization of semiconductor regions by pulsed laser light, however, can not be sufficiently accomplished in accordance with conventional techniques due to a sharp change in temperature during the laser exposure step. Because of this, there tends to remain in the semiconductor region a portion whose crystallinity is inadequate for appropriate carrier transportation so as to lower the reliability of the insulated gate thin film field effect transistors.